The compound: ##STR5## is known to have herbicidal activity. This herbicidal compound can be prepared from the dione: ##STR6## which has been prepared by condensation of acetoacetic acid and 3-ethylthio-butyraldehyde, followed by Michael addition with diethyl malonate, hydrolsis, and decarboxylation. Simplified synthetic routes to the above-described dione would be desirable, so that fewer reaction steps would be required, the use of expensive reagents (such as diethyl malonate) would be avoided, and other similar compounds could be readily prepared